Hydraulic steering system having auxiliary power source

ABSTRACT

A hydraulic steering system for a motor vehicle having a primary fluid pressure source and a secondary pressure source. The secondary source comprises a pump driven by the vehicle&#39;&#39;s transmission upon demand and which is inoperative when the primary pressure source is functioning properly.

United States Patentv Goodale [s41 HYDRAULIC STEERING SYSTEM HAVINGAUXILIARY POWER SOURCE [72] Inventor: William B. Goodale, Orchard Lake,

Mich.

[731 Assignee: Ford Motor Company, Dearborn,

Mich.

221 Filed: July 31, 1970 [21] Appl.No.: 64,130

Related US. Application Data [63] Continuation of Ser. No. 763,228,Sept. 27,

1968, abandoned.

[52] US. Cl. ..60/52'8, 180/792 [51] Int. Cl. ..FlSb 15/18, B62d 5/06[58] Field of Search ..60/52 S; 180/792 1 Oct. 10,1972

Primary Examiner-Edgar W. Geoghegan Attomey-John R. Faulkner andClifford L. Sadler [57] ABSTRACT A hydraulic steering system for a motorvehicle having a primary fluid pressure source and a secondary pressuresource. The secondary source comprises a pump [56] References Citeddriven by the vehicle's transmission upon demand and UNITED STATESPATENTS which is inoperative when the primary pressure source isfunctioning properly. 1,955,922 4/1934 Lamond ..60/52 S 2,323,519 7/1943 I Dean ..60/52 HC UX 11 Claims, 2 Drawing Figures 1 \ea W 4'0 .12 I42 I 24 I HYDRAULIC STEERING SYSTEM HAVING AUXILIARY POWER SOURCE Thisapplication is a continuation of application Ser. No. 763,228 filedSept. 27, 1968 for HYDRAULIC STEERING SYSTEM HAVING AUXILIARY POWERSOURCE and now abandoned.

BACKGROUND OF THE INVENTION Power steering for a motor vehicleisprovided to achieve two related objects. The power steering mechanismprovides a: power assist to reduce the steering effort required of thevehicle driver. Because the mechanism provides a power assist, it isalso possible to achieve the second object of reducing the steering gearratio. This functions to the drivers advantage by reducing the number ofturns of the steering wheel that are necessary to execute a particularmaneuver such as parking.

With the reduction in steering gear ratio there is an accompanyingreduction in mechanical advantage so that if a failure of the hydraulicpressure source should occur, considerable energy is required of thevehicle operator to turn the wheel. A power steering system in which thepressure source is not functioning is more difficult to manage than astandard manual steering system. This is due, in part, to the lowersteering gear ratio. a

In view of the state of the an, it is a principal object of the presentinvention to provide a motor vehicle hydraulic steering system having anauxiliary pump circuit that is automatically activated in the event of afailure in the main power steering pump circuit so that the vehicle maycontinue to be operated effectively by the driver.

BRIEF SUMMARY OF THE DISCLOSURE In the presently preferred embodiment ofthis invention, primary and auxiliary fluid pressure sources areprovided for operating a power steering gear. The vehicle has a powersteering pump driven by the engine which is in communication with thepower steering gear. Fluid flows from the outlet of the gear to the sumpof the primary pump circuit. An auxiliary pump has a piston which isdriven by the transmission output shaft. The secondary pump piston isheld in an inoperative position by a pilot device which is responsive tothe outlet pressure of the steering gear. When the primary pressuresource fails, the pilot piston moves to a position permitting thesecondary pump piston to be actuated by a cam on the transmission outputshaft. The secondary pump is in circuit with the steering gear and isisolated from the primary pump circuit by means of check valves.

BRIEF DESCRIPTION OF THE DRAWINGS The many objects and advantages of thepresent invention will become apparent upon consideration of thefollowing detailed discussion and the accompanying drawings in which:

FIG. 1 is a diagrammatic representation of a motor vehicle powersteering system according to the present invention; and

FIG. 2 is an elevational view in section of an auxiliary pump for thesystem of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to thedrawings wherein the presently preferred embodiment of this invention isillustrated FIG. 1 discloses, in diagrammatic form, a hydraulic powersteering system for a motor vehicle. The system of FIG. 1 includes aprimary pump 10 and an auxiliary pump 11 having appropriate circuitryconstructed to provide pressurized fluid to a power steering gear 12.

This steering gear unit 12 is of a known type having a movable pistonintegral with a worm. The worm moves upon displacement of the piston byfluid pressure applied to one side or the other thereof in a knownmanner.

The primary pressure source for the power steering gear 12 includes theprimary pump 10 which is driven by a belt 14 connected to the vehicleengine 16. A hydraulic line 18 conveys fluid pressure from the outlet ofthe primary pump 10 through a check valve 20. Hydraulic line 22 connectsthe check valve 20 with the power steering gear unit 12. Hydraulic line24 connects the outlet or the return flow port of the steering gear 12to the check valve 26. Line 28 joins the check valve 26 with the sump30. The circuit is completed by a hydraulic line 32 which conveys fluidfrom the sump 30 to the pump 10.

This portion of the circuit operates in a reasonably conventionalfashion with the pump 10 providing hydraulic fluid under pressure to thesteering gear unit 12 which, in turn, provides a power assist to theoperation of the steering gear.

In accordance with the present invention, auxiliary means is provided tobring hydraulic fluid under pressure to the steering gear in the eventthe primary pressure source should fail. In accordance with theinvention, the auxiliary circuit includes the auxiliary pump 11 which isdriven by the output shaft 36 of the vehicle transmission 38. Asindicated in the drawings, transmission 38 is connected to the engine16. The output of the pump 11 flows through a check valve 40 to which itis connected by means of a passage 42. Hydraulic line 44 connects thecheck valve 40 with a second check valve 46. A short hydraulic line 48taps into the line 22 of the power steering gear 12 and is connected tothe check valve 46. Line 50 is connected to the return line 24 leadingfrom the outlet of the power steering gear 10. Fluid flowing through thehydraulic line 50 passes through check valve 52 into the interior of thepump 1 l.

The construction of the auxiliary pump 11, check valves 40 and 52 andrelated structure is illustrated in greater detail in FIG. 2. In FIG. 2,the transmission 38 has a housing 56 which rotatably supports thetransmission. output shaft 36. A cam 58 is keyed to the shaft 36. The.housing 59 for the pump 11 issecured to the transmission housing 56 bybolts 61. The pump housing 59 is formed with a bore 60 in which a pumppiston 62 is slidably received. The pump piston 62 has a seal 64 at itsupper end in sliding engagement with the wall of the bore 60. A bearingplate 66 is secured to the end of the piston 62 for sliding engagementwith the rotating cam 58. A coil spring 68 biases the piston in adirection to place the bearing plate 66 in engagement with the cam 58.

The inlet for the pump 11 includes a bore 70 to which a fitting 72 issecured for connection with the hydraulic line 50. The check valve 52for the pump 11 comprises a valve element 74 that has a stem 76 securedto it. A coil spring 78 is interposed between the end of the stem 76 anda collar 80 which forms a stationary spring seat. The spring 78 urgesthe valve element 74 into a closed position against a valve seatmachined in the housing 59 as illustrated in FIG. 2.

The coil spring 78 of the check valve 52 lightly urges the element 74 toa seated position. When the pump piston 62 is moved toward the axis ofthe transmission output shaft 36 by the spring 68, the drop in pressurewithin pressure chamber 81 of the pump will cause the valve element 72to unseat and to permit fluid to flow into the bore 60. During apressure stroke of the piston 62, fluid within the bore will beprevented from returning to the inlet passage 70 by the check valve 52.

Check valve 40 is placed in the outlet of the pump 11. The check valve40 comprises a ball-shape valve element 82 that is pressed by a spring84 to a closed position against a valve seat. Passage 42 conveys fluidto the check valve 40 from the chamber 81 of the pump 11. The outlet ofthe check valve 40 is constructed at 86 to receive a fitting forattachment of the hydraulic line 44.

A pilot piston 88 is positioned within a bore 90 formed in the housing59. The piston 88 has a stem portion 92 that is constructed to engage anotch 94 formed on the side of the secondary pump piston 62. A chamber96 is formed on the back side of the piston 88 by means of a cap 98which seals the bore 90. A coil spring 100 is interposed between thehousing 59 and the pilot piston 88 and it exerts a force tending to movethe portion 92 of pilot piston 88 outwardly away from the notch 94 inthe pump piston 62. The chamber 96 communicates with the inlet bore 70of the pump 11 by means of a passage 102 drilled in the housing 59. Withthis construction when the hydraulic fluid in the inlet bore 70 ispressurized, chamber 96 will also be pressurized thereby causing thepiston 88 to move into engagement with the pump piston 62. When the nose92 of the pilot piston 88 is seated in the groove 94, the pump piston 62will be held outwardly out of engagement with the cam 58. This willoccur whenever the inlet pressure to the pump 11 is of appropriatemagnitude. It will be noted from FIG. 1 that the inlet pressure to thepump 11 is also the outlet pressure of the power steering gear 12.

A short passage 104 connects the pressure chamber 81 of the pump piston62 with a pressure release valve 106. The pressure release valve is incommunication with the passage 102 at the inlet of the pump.

OPERATION During normal or conventional operation, the primary powersteering pump is the sole pump providing pressure fluid for the powersteering gear 12. The primary pump 10 is driven by the motor 16 anddelivers fluid under pressure through the lines 18 and 22 to the powersteering gear 10. Fluid returns to the sump 30 by means of the lines 24and 28. Check valves 26 and prevent flow of fluid in the oppositedirection. In addition, check valve 46 prevents flow of fluid to thesecondary pressure source.

Thus, during normal operation fluid flows from the primary pump 10across the check valve 20 to the steering gear 10 and returns to thereservoir sump 30 after flowing across the check valve 26. The pressurein return line 50 which is equal to both the pressure differentialacross the valve 26 and the pressure at the outlet of the steering gear12 is sensed on the area of the pilot piston 88 of the secondary pumpassembly 11. This pressure moves the pilot piston 88 inwardly againstthe spring allowing the piston stem 92 to engage the notch 94 in thepump piston 62. This engagement holds the pump piston 62 away from thecam 58 and in this condition, the secondary pump assembly 1 1 isinoperative.

When there is a failure in the primary pump 10 or of the elements thatdrive the pump 10, the pressure differential across the check valve 26will decrease and thereby reduce the force on the pilot piston 88 ofauxiliary pump assembly 11. This allows the piston spring 100 to movethe piston 88 outwardly drawing the piston stem 92 out of engagementwith the pump piston 62. The piston spring 68 returns the pump piston 62into engagement with the cam 58 and as the cam rotates pumping willoccur. Fluid will then flow across the check valves 40 and 46 throughthe steering gear assembly 12, and returning to the pump 11 across thecheck valve 52. Pumping continues as long as the transmission driveshaft rotates, Thus, if the primary pump 10 should cease to operate dueto a failure of the engine 16 the auxiliary pump 11 would commence tofunction and produce fluid pressure for the steering gear 12 during theperiod when the vehicle is coasting to a halt.

The fluid line 50 from the steering gear assembly 12 to the auxiliarypump 11 serves as its fluid reservoir. Maximum flow of pump 11 iscontrolled by the force of the piston spring 68 which will hold thepiston 62 to the cam 58 up to a predetermined speed of the cam.

Valve 104 serves as a pressure relief valve for pump assembly 11 anddetermines the maximum pressure of the auxiliary circuit.

SUMMARY In accordance with the present invention, a power steeringsystem for a motor vehicle is provided having a primary fluid pressuresource and a secondary fluid pressure source that operates only when theprimary source fails. The secondary source is driven by the transmissionoutput shaft and has a pump piston which engages the cam on the shaftonly when there is a failure or lack of pressure in the primary circuit.

While the invention has been illustrated in the preferred embodiment, itwill be clear to those skilled in the art that changes and modificationsmay be made without departing from the scope of the invention.

I claim:

1. A dual fluid supply circuit for a fluid operated mechanism having afluid inlet and a fluid outlet, comprising a main normally driven fluidsupply pump and an auxiliary normally at rest fluid supply pump, each ofsaid pumps having a fluid discharge line and a fluid return line, meansconnecting said discharge lines in parallel to said inlet, meansconnecting said return lines in parallel to said outlet of saidmechanism, control means isolating said main pump from said auxiliarypump, means responsive to the fluid pressure in said return line-of saidauxiliary pump and constructed to permit the operation of said auxiliarypump when the fluid pressure in said return line falls below a presetminimum.

2. A dual fluid supply circuit for a fluid operated mechanism accordingto claim 1 and including:

said last mentioned responsive means being constructed to prevent theoperation of said auxiliary pump when said fluid pressure in said returnline isabove a preset minimum.

3. A power steering system comprising a power steering unit having afluid inlet and a fluid outlet, comprising a primary normally drivenfluid supply pump having a fluid discharge line and a fluid return line,an auxiliary fluid supply pump having a fluid discharge line and a fluidreturn line, means connecting said discharge lines in parallel to saidinlet, means connecting said return lines in parallel to said outlet,control means isolating said primary pump from said auxiliary pump,means responsive to the fluid pressure in said return line of saidauxiliary pump and constructed to permit the operation of said auxiliarypump when the fluid pressure in said return line falls below apresetminimum.

4. A power steering system according to claim 3 and including:

said last mentioned responsive means being constructed to prevent theoperation of said auxiliary pump when said fluid pressure in said returnline is above a preset minimum.

5. A power steering system comprising a power steering unit having afluid inlet and a fluid outlet, comprising a primary normally drivenfluid supply pump having a fluid discharge line and a fluid return line,an auxiliary fluid supply pump having a fluid discharge line and a fluidreturn line, means connecting said discharge lines in parallel to saidinlet, means connecting said return lines in parallel to said fluidoutlet, control means isolating said primary pump from said auxiliarypump, means responsive to the fluid pressure in said return line of saidauxiliary pump and constructed to prevent the operation of saidauxiliary pump when said fluid pressure in said return line is above apreset minimum.

6. A dual fluid supply circuit for a fluid operated mechanism having afluid inlet and a fluid outlet, comprising a normally operative primaryfluid pressure source and a normally at rest auxiliary fluid pressuresource, each of said fluid pressure sources having a fluid dischargeline and a fluid return line, means connecting both said discharge linesto said inlet of said mechanism, means connecting both said return linesto said outlet of said mechanism, control means isolating said primaryfluid pressure source from said auxiliary fluid pressure source, saidcontrol means comprising a check valve in each of said fluid dischargeline and said fluid return line of said primary source, said controlmeans also comprising a check valve in each of said fluid discharge lineand said fluid return line of said auxiliary source, fluid pressureresponsive means connected to said outlet of said mechanism and saidauxiliary source, said pressure responsive means being constructed toenable the operation of said normally at rest auxiliary source when thefluid pressure at said outlet of said mechanism does not exceed a presetminimum.

7. A dual fluid supply circuit for a fluid operated mechanism accordingto claim 6 and including:

said fluid pressure responsive means being further constructed toprevent the operation of said auxiliary source when the fluid pressureat said outlet of said mechanism exceeds a preset minimum.

8. A power steering system comprising a power steering unit having afluid inlet and a fluid outlet, a normally operative primary fluidpressure source having a fluid discharge line and a fluid return line, anormally at rest auxiliary fluid pressure source having a fluiddischarge line and a fluid return line, means connecting both saiddischarge lines to said fluid inlet of said power steering unit, meansconnecting both said return lines to said fluid outlet of said powersteering unit, control means isolating said primary source from saidauxiliary source, said control means comprising a check valve in each ofsaid fluid discharge line and said fluid return line of said auxiliarysource, fluid pressure responsive means connected to said outlet of saidpower steering unit and said auxiliary source, said pressure responsivemeans being constructed to enable the operation of said normally at restauxiliary source when the fluid pressure at said outlet of said powersteering unit does not exceed a preset minimum.

9. A power steering system according to claim 8 and including:

said fluid pressure responsive means being further constructed toprevent the operation of said auxiliary source when the fluid pressureat said outlet of said power steering unit exceeds a preset minimum.

10. A power steering system comprising a power steering unit having afluid inlet and a fluid outlet, comprising a normally operative primaryfluid pressure source having a fluid discharge line and a fluid returnline, a normally at rest auxiliary fluid pressure source having a fluiddischarge line and a fluid return line, means connecting both saiddischarge lines to said inlet, means connecting both said return linesto said outlet, control means isolating said primary source from saidauxiliary source, said control means comprising a check valve in each ofsaid fluid discharge line and said fluid return line of said primarysource, said control means also comprising a check valve in each of saidfluid discharge line and said fluid return line of said auxiliarysource, fluid pressure responsive means connected to said outlet of saidpower steering unit and said auxiliary source, said pressure responsivemeans being constructed to prevent the operation of said normally atrest auxiliary source when the fluid pressure at said outlet of saidunit exceeds a preset minimum.

11. A dual fluid supply system having a fluid operated mechanism with afluid inlet and a fluid outlet comprising a normally operative primaryfluid pressure source having a fluid inlet and a fluid outlet, firstmeans connecting the fluid outlet of said primary pressure source to thefluid inlet of said mechanism, second means connecting said fluid outletof said mechanism to a check valve, third means connecting said checkvalve to said fluid inlet of said primary source, a normallyat restauxiliary pressure source having a fluid inlet and a fluid outlet, saidfluid outlet of said auxiliary pressure source being connected to thefluid inlet of said mechanism, said fluid inlet of said auxiliarypressure source being connected to said second means, fluid pressureresponsive means connected to the fluid inlet of said auxiliary pressuresource and constructed to enable the operation of said auxiliarypressure source when the fluid pressure in said fluid inlet of saidauxiliary pressure source is below a preset minimum.

1. A dual fluid supply circuit for a fluid operated mechanism having afluid inlet and a fluid outlet, comprising a main normally driven fluidsupply pump and an auxiliary normally at rest fluid supply pump, each ofsaid pumps having a fluid discharge line and a fluid return line, meansconnecting said discharge lines in parallel to said inlet, meansconnecting said return lines in parallel to said outlet of saidmechanism, control means isolating said main pump from said auxiliarypump, means responsive to the fluid pressure in said return line of saidauxiliary pump and constructed to permit the operation of said auxiliarypump when the fluid pressure in said return line falls below a presetminimum.
 2. A dual fluid supply circuit for a fluid operated mechanismaccording to claim 1 and including: said last mentioned responsive meansbeing constructed to prevent the operation of said auxiliary pump whensaid fluid pressure in said return line is above a preset minimum.
 3. Apower steering system comprising a power steering unit having a fluidinlet and a fluid outlet, comprising a primary normally driven fluidsupply pump having a fluid discharge line and a fluid return line, anauxiliary fluid supply pump having a fluid discharge line and a fluidreturn line, means connecting said discharge lines in parallel to saidinlet, means connecting said return lines in parallel to said outlet,control means isolating said primary pump from said auxiliary pump,means responsive to the fluid pressure in said return line of saidauxiliary pump and constructed to permit the operation of said auxiliarypump when the fluid pressure in said return line falls below apresetminimum.
 4. A power steering system according to claim 3 andincluding: said last mentioned responsive means being constructed toprevent the operation of said auxiliary pump when said fluid pressure insaid return line is above a preset minimum.
 5. A power steering systemcomprising a power steering unit having a fluid inlet and a fluidoutlet, comprising a primary normally driven fluid supply pump having afluid discharge line and a fluid return line, an auxiliary fluid supplypump having a fluid discharge line and a fluid return line, meansconnecting said discharge lines in parallel to said inlet, meansconnecting said return lines in parallel to said fluid outlet, controlmeans isolating said primary pump from said auxiliary pump, meansresponsive to the fluid pressure in said return line of said auxiliarypump and constructed to prevent the operation of said auxiliary pumpwhen said fluid pressure in said return line is above a preset minimum.6. A dual fluid supply circuit for a fluid operated mechanism having afluid inlet and a fluid outlet, comprising a Normally operative primaryfluid pressure source and a normally at rest auxiliary fluid pressuresource, each of said fluid pressure sources having a fluid dischargeline and a fluid return line, means connecting both said discharge linesto said inlet of said mechanism, means connecting both said return linesto said outlet of said mechanism, control means isolating said primaryfluid pressure source from said auxiliary fluid pressure source, saidcontrol means comprising a check valve in each of said fluid dischargeline and said fluid return line of said primary source, said controlmeans also comprising a check valve in each of said fluid discharge lineand said fluid return line of said auxiliary source, fluid pressureresponsive means connected to said outlet of said mechanism and saidauxiliary source, said pressure responsive means being constructed toenable the operation of said normally at rest auxiliary source when thefluid pressure at said outlet of said mechanism does not exceed a presetminimum.
 7. A dual fluid supply circuit for a fluid operated mechanismaccording to claim 6 and including: said fluid pressure responsive meansbeing further constructed to prevent the operation of said auxiliarysource when the fluid pressure at said outlet of said mechanism exceedsa preset minimum.
 8. A power steering system comprising a power steeringunit having a fluid inlet and a fluid outlet, a normally operativeprimary fluid pressure source having a fluid discharge line and a fluidreturn line, a normally at rest auxiliary fluid pressure source having afluid discharge line and a fluid return line, means connecting both saiddischarge lines to said fluid inlet of said power steering unit, meansconnecting both said return lines to said fluid outlet of said powersteering unit, control means isolating said primary source from saidauxiliary source, said control means comprising a check valve in each ofsaid fluid discharge line and said fluid return line of said auxiliarysource, fluid pressure responsive means connected to said outlet of saidpower steering unit and said auxiliary source, said pressure responsivemeans being constructed to enable the operation of said normally at restauxiliary source when the fluid pressure at said outlet of said powersteering unit does not exceed a preset minimum.
 9. A power steeringsystem according to claim 8 and including: said fluid pressureresponsive means being further constructed to prevent the operation ofsaid auxiliary source when the fluid pressure at said outlet of saidpower steering unit exceeds a preset minimum.
 10. A power steeringsystem comprising a power steering unit having a fluid inlet and a fluidoutlet, comprising a normally operative primary fluid pressure sourcehaving a fluid discharge line and a fluid return line, a normally atrest auxiliary fluid pressure source having a fluid discharge line and afluid return line, means connecting both said discharge lines to saidinlet, means connecting both said return lines to said outlet, controlmeans isolating said primary source from said auxiliary source, saidcontrol means comprising a check valve in each of said fluid dischargeline and said fluid return line of said primary source, said controlmeans also comprising a check valve in each of said fluid discharge lineand said fluid return line of said auxiliary source, fluid pressureresponsive means connected to said outlet of said power steering unitand said auxiliary source, said pressure responsive means beingconstructed to prevent the operation of said normally at rest auxiliarysource when the fluid pressure at said outlet of said unit exceeds apreset minimum.
 11. A dual fluid supply system having a fluid operatedmechanism with a fluid inlet and a fluid outlet comprising a normallyoperative primary fluid pressure source having a fluid inlet and a fluidoutlet, first means connecting the fluid outlet of said primary pressuresource to the fluid inlet of said mechanism, second mEans connectingsaid fluid outlet of said mechanism to a check valve, third meansconnecting said check valve to said fluid inlet of said primary source,a normally at rest auxiliary pressure source having a fluid inlet and afluid outlet, said fluid outlet of said auxiliary pressure source beingconnected to the fluid inlet of said mechanism, said fluid inlet of saidauxiliary pressure source being connected to said second means, fluidpressure responsive means connected to the fluid inlet of said auxiliarypressure source and constructed to enable the operation of saidauxiliary pressure source when the fluid pressure in said fluid inlet ofsaid auxiliary pressure source is below a preset minimum.